The Contractor will serve as the Data Coordinating Center in a multicenter clinical trial to determine whether tight (scrict) control of blood glucose is effective in preventing or ameliorating the early vascular complications of insulin-dependent diabetes mellitus. The Data Coordinating Center will participate with the National Arthritis, Diabetes, and Digestive and Kidney Diseases and approximately twenty clinical centers in all phases of this trial. The Contractor, in conjunction with the NIADDK Project Office, will have responsibility for the operational conduct of the trial and for data analysis. The approximately twenty treatment centers supported under cooperative agreement research grants will be the data-contributing medical institutions responsible for the clinical conduct of this study. Central support services (e.g., central laboratories or fundus photography reading center), as may be necessary to the conduct of this trial, may be administered under subcontract to the Data Coordinating Center.